Balanced diet — seven components
A balanced diet contains carbohydrates, fats, proteins, vitamins, mineral ions, fibre (roughage) and water in the correct proportions — not equal amounts of everything. Carbohydrates (sugars and starch) supply energy; fats give energy storage, insulation and protection of organs; proteins give growth and repair, enzymes and antibodies; fibre stimulates peristalsis; water transports substances, is the medium for reactions and cools the body by sweating.
Deficiency pairs — scurvy C, rickets D
Scurvy follows a lack of vitamin C, which is needed to make collagen in skin, gums and blood vessel walls — hence bleeding gums, slow wound healing and painful joints. Rickets follows a lack of vitamin D, which is needed to absorb calcium from the small intestine; without it bones fail to mineralise and become soft, weak and bowed in children. Memory aid: C for Citrus, D for the sun that lets skin make it.
Mineral ions — calcium and iron
Calcium builds and maintains strong bones and teeth and is required for muscle contraction; sources are dairy (milk, cheese, yoghurt), leafy green vegetables and fortified foods. Iron is a component of haemoglobin, the oxygen-carrying protein in red blood cells; sources are red meat, liver, spinach and lentils. Too little iron causes anaemia — fewer functional red blood cells, so less oxygen carried, giving fatigue and pallor.
Drawn from real examiner reports.
Swapping scurvy and rickets
Scurvy is a lack of vitamin C; rickets is a lack of vitamin D. Swapping the pair is the most heavily penalised error on diet questions across recent sittings. "Not enough vitamins" earns nothing either — the specific vitamin must be named. The mark-scheme form for "state the cause" is "lack of / insufficient vitamin C" or "lack of / insufficient vitamin D".
Vitamin deficiency diseases mixed up: rickets caused by lack of vitamin D; scurvy caused by lack of vitamin C (not iron). (s23 Paper 32 Q4b; s22 Paper 13 Q13)
Blaming scurvy on iron deficiency
Iron deficiency causes anaemia — too little haemoglobin, so less oxygen is carried, giving fatigue and pallor. It does not cause scurvy. Keep the three pairings separate and rehearsed: vitamin C → scurvy, vitamin D → rickets, iron → anaemia. Examiners record candidates attributing scurvy to iron in both written answers and multiple-choice options.
Vitamin deficiency diseases mixed up: rickets caused by lack of vitamin D; scurvy caused by lack of vitamin C (not iron). (s23 Paper 32 Q4b; s22 Paper 13 Q13)
Fibre aids egestion, not excretion
Egestion removes undigested food (faeces) through the anus — fibre adds bulk, stimulates peristalsis and prevents constipation. Excretion removes the waste products of metabolism ( via the lungs, urea via the kidneys) and has nothing to do with fibre. "Fibre helps excretion" or "fibre removes waste products" scores zero.
Fibre function: confused "excretion" with "egestion." Fibre aids movement of food through the alimentary canal and helps prevent constipation (egestion of faeces). (s23 Papers 11/12 Q15; Paper 32 Q4c ii) Egestion (not excretion) occurs at the anus. (s22 Paper 31 Q6a; Paper 32 Q6a)
Naming a food group, not a named food
For "state a dietary source of calcium", name the food: milk, cheese, yoghurt, leafy green vegetables, tinned fish with bones or fortified cereals. Examiners report that candidates rarely offer dairy foods, the richest source. "Vegetables", "healthy food", "meat" or "fruit" alone are too vague. The same rule applies to iron: red meat, liver, spinach, lentils.
Calcium source: candidates rarely gave dairy foods (e.g., cheese); calcium role is in bones and teeth. (s23 Paper 32 Q4a)
Blaming rickets on dietary calcium
"A lack of calcium in the diet causes rickets" is not the mark-scheme cause. The tested cause is a lack of vitamin D, which is needed to absorb calcium from the small intestine — a diet can contain plenty of calcium and rickets still develops. Always route the explanation through vitamin D, then calcium absorption, then soft bones.
Calling protein the main energy source
Carbohydrates are the primary energy source and fats are the energy store. Protein's function is growth and repair of cells and making enzymes and antibodies. Listing protein as the body's main energy supply is a standard multiple-choice distractor and loses the mark in written answers.
Vague roles: "strong bones", "for blood"
Mark schemes want the precise form. Calcium is for bones and teeth (plus muscle contraction) — "makes bones strong" alone may not be credited. Iron is a component of haemoglobin; "iron helps carry oxygen" is too loose on its own. Fats are for energy storage, insulation and protection of organs, not simply "energy".
Calcium source: candidates rarely gave dairy foods (e.g., cheese); calcium role is in bones and teeth. (s23 Paper 32 Q4a)
Give the specific role, not "energy"
Fats = energy storage, insulation, protection of organs (not "gives you energy"). Proteins = growth and repair, enzymes and antibodies. Vitamin D = absorption of calcium, prevents rickets. Iron = component of haemoglobin. Fibre = stimulates peristalsis, prevents constipation.
Three-step scaffold for "explain why"
(1) State what the nutrient is needed for. (2) State the consequence when it is missing. (3) Name the resulting condition. Example: vitamin D is needed to absorb calcium from food; without it too little calcium is absorbed; bones become soft and weak, causing rickets.
Test MCQ options against the fixed pairs
Run every option past the four pairings — scurvy–vitamin C, rickets–vitamin D, iron–haemoglobin, calcium–bones and teeth. Eliminate anything that swaps them, blames rickets on dietary calcium alone, or makes protein the main energy source.
Balanced diet: a diet that contains all seven dietary components in the correct proportions for healthy functioning of the body. The seven components are: carbohydrates, fats, proteins, vitamins, mineral ions, fibre (roughage) and water.
Note: "balanced" does NOT mean equal amounts of each — it means the right proportions for health (more carbohydrates than fat, for example). An individual's needs vary with age, sex, pregnancy and level of physical activity.
Define a balanced diet.
State the seven components of a balanced diet.
